Improved Phase Characterization of Far-Regional Body Wave Arrivals in Central Asia
Abstract
At far-regional and near-teleseismic distances the early body-wave coda contains information that is potentially useful to monitoring seismologists. However, waveforms from this distance range are typically under-utilized because of propagation complexities that cause significant difficulties in seismogram interpretation. For example, the first approx. 20 seconds of a far-regional seismogram often include multi-pathed arrivals caused by the interaction of the wavefield with upper mantle discontinuities at 220 km, 410 km and 660 km depth. Depth phases (e.g., pP. pP410. sP, sP410, etc.) also add complexity to the early part of the seismogram since they can constructively or destructively interfere with the primary phase arrivals. Array observations from earthquakes in central Asia regularly exhibit a variety of complex phase phenomena, such as back-azimuth anomalies, emergent or late-arriving first arrivals, large amplitude secondary arrivals, and interference phenomena between upper mantle arrivals and depth phases. We have developed array-based methods to improve the characterization of primary and early coda phase arrivals observed at far-regional and near-teleseismic distances. These techniques include improved signal processing to accurately measure the delay times (r's) and slownesses (p's) of primary and secondary phases from small-aperture arrays. We use these r-p measurements to develop representative crust and mantle velocity-depth profiles and suites of synthetic seismograms through those models. Then we use the processed array beams to derive `wavefield templates'; i.e., grouped observations with similar phase characteristics. We analyze these wavefield templates by comparing them with synthetics, looking for quantitative explanations for the phase behaviors we observe. Our approach results in a methodology that improves phase characterization and yields earth models that more accurately predict the succession of expected arrivals.
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 30, 2008
- Accession Number
- ADA487737
Entities
People
- Aaron Ferris
- Anastasia Stroujkova
- Delaine Reiter